The present invention relates to the field of vehicle suspensions, and more specifically relates to an active type suspension for a vehicle such as an automobile.
In a conventional type of suspension for a vehicle such as an automobile, with the object of damping the shock input from the road surface to the vehicle wheel and transmitted to the vehicle body and further of improving the comfort of the ride of the vehicle, typically suspension springs are incorporated which support the weight of the vehicle and allow a relative movement principally in the vertical direction between the vehicle wheel and vehicle body, thus absorbing the road shocks as positional energy by elastic deformation. The load on such a suspension spring, that is, the load acting between a particular vehicle wheel and the vehicle body, is determined mechanically by the weight of the vehicle body (the proportion thereof which is resting upon this spring) and the relative positional relation between the particular vehicle wheel and the vehicle body, and this fluctuates according to the running state of the vehicle. For example, when the vehicle is turning, or during sharp acceleration or deceleration, the vehicle body is urged by its own inertia relative to the vehicle wheel, and as a result the load acting between the vehicle wheel and the vehicle body changes, the elastic deformation amount of the suspension spring changes, and undesirable swaying or changes in attitude such as roll or nose dive are typically produced.
Techniques conventionally applied in order to reduce the swaying and attitude changes of the vehicle, and in order to ensure stable driving characteristics, include the incorporation of stabilizers in the suspension for a vehicle such as an automobile, and the provision of progressive spring characteristics for the suspension spring. Since, however, these techniques only passively reduce the vehicle swaying or attitude change, the swaying or attitude change of the vehicle cannot be satisfactorily completely reduced. In order moreover to ensure a satisfactory ride for the vehicle while improving driving stability by the above methods, there is required complicated calculation and design of the suspension structure, and fine tuning of the suspension springs and shock absorbers is necessary. Accordingly, in the case of wear over a long service life, the proper stability of the vehicle cannot be assured.
As an active vibration damping method and device for a wheeled vehicle such as an automobile, there has been disclosed in Japanese Patent Laid Open Publication No. Sho 54-55913 (1979), which it is not intended hereby to admit as prior art to the present application except to the extent otherwise mandated by law, a system in which, in a vehicle in which the vehicle body mass is disposed above the mass of each of a number of vehicle wheels with a servo cylinder for producing a force operated by a valve interposed therebetween, characterised in that the valve is an electrohydraulic valve driven by an eletrohydraulic means, and as measurement signals for this purpose are used the relative spacing between the vehicle body and vehicle wheel, the relative velocity during relative motion of the vehicle body and vehicle wheel, and the pressure difference in the servo cylinder. Since, however, this method and device presuppose relative displacement between vehicle body and vehicle wheel, it is not possible by this method and device to maintain a substantially constant vehicle attitude.